Brain electrical activity topographical mapping

ABSTRACT

An apparatus for monitoring and operating on brain input activity signals to provide topographical maps characteristic of patient brain activity. The apparatus senses the brain input activity signals and processes the signals to provide detailed information on patient brain activity. Complete topographical maps of the patient brain are activity constructed by a line-by-line interpolation method. A color coded scale adjacent the topographical map is utilized to provide additional information on patient brain activity. The user has a number of options available to select various information for display and analysis.

The present invention relates generally to an apparatus and method fordisplaying a topographical map of brain electrical activity of apatient, and more particularly to a novel method and apparatus forperforming rapid manipulation of data using computer software to provideline-by-line interpolation of input activity signals and output of aplurality of topographical maps having a variety of informationcharacteristic of brain electrical activity.

Information on brain electrical activity is typically obtained byperforming evoked potential (EP) response measurements andelectroencephelogram (EEG) measurements. Such measurements often yield aset of complicated time varying outputs. A detailed and thoroughanalysis of these complicated outputs requires computer manipulation todetermine differences of brain electrical activity of a selected patientcompared to a representative normal population. A number of limitationscurrently exist for computer manipulation and analysis of these brainelectrical activity measurements. In prior computerized apparatus thebrain electrical activity measurements have been performed using a largenumber of system components to carry out the tasks of measurement,analysis and display of data. Consequently, such computerized systemsare costly to purchase and maintain, and the system is unnecessarilycomplicated. Furthermore, prior computerized systems for measurement andoutput of brain electrical activity generate the topographical mapswithout clearly associating all the appropriate data and withoutmanipulating and displaying the optimum available data combinations. Forexamples of various prior approaches, see, U.S. Pat. Nos. 4,408,616;4,417,591; 4,201,224 and 4,421,122; which are incorporated by referenceherein. Therefore, in order to obtain the maximum benefit andunderstanding from the measured brain electrical activity, it isessential to manipulate, use and display the data to the viewer in thebest manner possible.

BREIF SUMMARY OF THE INVENTION

One of the primary objects of the invention is to provide an improvedapparatus and method for displaying a topographical map of brainelectrical activity.

A more particular object of the invention is to provide a novelapparatus and a method for manipulating brain electrical activitysignals using computer software to provide a video display oftopographical maps of brain electrical activity.

Another object of the invention is to provide a novel method andapparatus for generating a video display of brain electrical activitysignals interpolated and output for display on a line-by-line basis forpositions between, as well as at, the electrode sensors on a patient'shead.

An additional object of the invention is to provide an improved methodand apparatus for displaying a topographical map of brain electricalactivity signals and including in the display a fixed color code scalewherein each color in the topographical map has a relative valuedetermined by correlation with each color in the fixed color scale.

Another object of the invention is to provide a method and apparatus forsimultaneously displaying a plurality of topographical maps of differentselectable states of brain electrical activity signals.

A further object of the invention is to provide an improved method andapparatus for increasing the rate of display of topographical maps ofbrain electrical activity signals by interlacing the output to thedisplay memory of every other pixel line in each of the topographicalmaps of brain electrical activity.

In accordance with the invention an apparatus and method for measuringand displaying topographical maps of brain electrical activity usescomputer software to generate interpolated outputs of the brainelectrical activity signals and to carry out additional analysis andthen output the results to a display processing unit. A user can selectfor display a plurality of the topographical maps which illustratevarious characteristics of brain electrical activity signals, such asevoked potential (EP) response information and electroencephelogram(EEG) information. The brain electrical activity is measured byelectrode sensors which generate input activity signals. These inputactivity signals are interpolated line-by-line to generate an expandedfiner matrix of interpolated values. Interpolation is selectivelyperformed every other pixel line in the interlace mode of constructingthe topographical map. The display of characteristic data includes acolor code scale and associated numerical values for determining therelative magnitudes of regions of the topographical map. In addition tothe topographical maps, individual characteristic waveforms and otherassociated parameters can be simultaneously output to a video display orprinter for comparison and association with the topographical maps.

Further objects and advantages of the present invention, together withthe organization and manner of operation thereof, will become apparentfrom the following detailed description of the invention when taken inconjunction with the accompanying drawings wherein like referencenumerals designate like elements throughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of an apparatus for measuring brainelectrical activity signals and for displaying topographic mapscharacteristic thereof, and FIGS. 1BA, 1BB is a functional block diagramshowing the flow through the apparatus of the measured input activitysignals;

FIG. 2 shows a top view of positions of an electrode sensor arrangementwith respect to a patient head outline.

FIG. 3 is an array of electrode sensors and a superimposed image of aline-by-line interpolation of signals for the array;

FIGS. 4A and 4B are block diagrams of two alternative methods forline-by-line interpolation and output of signals;

FIG. 5 is a display output of evoked potential (EP) responsemeasurements showing a topographical map, associated waveforms forselected electrode sensor locations and a vertically positioned colorcode scale;

FIG. 6 is a block diagram of a noise signal evaluation procedure; and

FIG. 7 is a display output of a plurality of topographical maps ofevoked potential (EP) response measurements integrated over the timeintervals shown.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings, and in particular to FIG. 1A, a blockdiagram of a brain electrical activity mapping apparatus constructed inaccordance with one embodiment of the present invention is indicatedgenerally at 10. The brain electrical activity mapping apparatus(hereinafter referred to as the apparatus 10) includes sensor means,such as, for example, a set of electrode sensors 12 (for example, Grassgold cup manufactured by Grass Corporation) arranged on the top of apatient's head 13. In FIG. 2 is shown an enlarged detail of a preferredarrangement for a rectangular array or matrix of twenty-one of theelectrode sensors 12 positioned on the patient's head 13. Thearrangement illustrates one acceptable variety selected from variousconventional international formats. In response to brain electricalactivity the electrode sensors 12 generate input activity signals 14.

In selected operating modes of the apparatus 10, such as in measurementof evoked potential (hereinafter "EP") response, a stimulus 16 is alsoapplied to the patient, and in response to the stimulus 16 the resultingbrain electrical activity is sensed by the electrode sensors 12. Adetailed discussion of EP response measurements is set forth in Duffy etal., "Brain Electrical Activity Mapping (BEAM): A Method for Extendingthe Clinical Utility of EEG and Evoked Potential Data," Annals ofNeurology 5, Apr., 1979, pp. 209-231; which is incorporated by referenceherein. The type of stimulus 16 used in EP response measurements is, forexample, a strobe light, a sound (such as a click generator) or asomatosensory stimulus, such as mild electrical shock. These stimuli 16can be periodic, aperiodic and can also be combinations of eachavailable type of the stimulus 16. In the illustrated embodiment of FIG.1A, the stimulus 16 is controlled responsive to a control signal 18 froma main computer, such as a microprocessor unit 22. The type of stimulus16 is selected by a user input, such as a keyboard 23. In alternativeforms of the invention, the stimulus 16 is provided responsive to astimulus controller 20 which is a separate microcomputer or is a remotecontrol source.

In other modes of operation of the apparatus 10, such as inelectroencephelogram (hereinafter "EEG") measurements, the stimulus 16is not applied to the patient. However, the measurement of brainelectrical activity in the EEG mode otherwise follows substantially thesame steps as for EP measurement. Therefore, in general as shown in FIG.1A, the sensed input activity signal 14 is output from the electrodesensors 12 to processing means which includes an analog multiplexer 24,an amplifier 26 and an analog to digital converter (A/D) 28. If a Grassor Beckman polygraph is used, the electrode sensors 12, the multiplexer24 and the amplifier 26 are included in the polygraph.

In the illustrated embodiment the amplifier 26 comprises a plurality oftwenty-one amplifiers, each connected to an associated one of theelectrode sensors 12. The multiplexer 24 accepts from the amplifier 26each of the amplified input activity signals 14, and outputs each ofthese input activity signals 14 in serial fashion to the A/D converter28 (for example, a Dual Systems AIM 12). The A/D converter 28 providesto the microprocessor unit 22 an amplified and digitized, or aconverted, form of the input activity signal 14. In general, processingmeans includes those components of the apparatus 10 which operate on thesignals output by the electrode sensors 12 to provide the amplified anddigitized form of the input activity signals 14.

The microprocessor unit 22 in FIG. 1A can be any one of a plurality ofcommercially available computers, such as, for example, a Zenith Z-100,which uses an 8088 central processor chip (see, Intel Component DataCatalog, January 1982, pp. 8-25 to 8-51, which is incorporated byreference herein). The Zenith Z-100 also includes the keyboard 23, adisplay processing unit (hereinafter "DPU") 39 which will be describedin detail hereinafter, a disk drive (not shown) and on board randomaccess memory (hereinafter "RAM") 30, and PROM and ROM (not shown)memories. The microprocessor unit 22 controls collection, manipulationand output of the input activity signals 14. In a preferred embodiment,the microprocessor unit 22 includes the RAM 30 which functions in partas an averaging means for storing at predetermined locations a runningaccumulation of the plurality of input activity signals 14. Themicroprocessor unit 22 adds each new incoming value for the signals 14to the previous value and stores the total in the RAM 30 at thepredetermined locations. This accumulation of the amplified andconverted input activity signals 14 results in statistical averaging ofthe input activity signals 14 which improves the signal to noise ratio.Under typical operating conditions one to ten minutes of data averagingis desirable to obtain statistically meaningful values for the inputactivity signals 14.

In a preferred embodiment of the invention, the apparatus 10 controlsdata gathering and analysis responsive to software programs stored on adisk or tape 29, and the programs are read into the RAM 30 and executedby the microprocessor unit 22. The user interacts with themicroprocessor unit 22 through input means to supply an input signalresponsive to a user input. Examples of input means include the keyboard23, a light pen 34 and a mouse 36. The user can also supply an inputsignal by transfer of information already stored on a disk storage unit27 or stored in the disk or tape 29, or stored in a memory external tothe apparatus 10, such as, for example, a remote computer memory (notshown). These various input means enable setting of variables such asthe time period of data taking, the number and type of the stimuli 16and the desired software programs to manipulate the data for output anddisplay for user analyzation.

The operation of the apparatus 10 as illustrated in FIG. 1A can bebetter understood by reference to the procedural and signal flow diagramof FIG. 1BA and 1BB. As illustrated in FIG. 1BA, the apparatus 10 in thefirst decisional block has been initialized with user selectedparameters or default parameters, and a mode of operation is selected.If the EP response mode is selected, then a predefined stimuli 16 isapplied to the patient as a first step. However, if the EEG mode isselected, then there is no externally applied predefined stimuli 16, andthe electrode sensors 12 detect EEG signals directly from the patient'shead 13. In any event, whether the signals originate from the patient asan EEG signal or as an EP response signal, the next step is directed topreprocessing the outputs from the electrode sensors 12. Thispreprocessing can include, for example, a number of steps, includingamplification, hardware filtering, software filtering and fast Fouriertransformation.

The preprocessed outputs from the electrode sensors 12 are thendigitized, and the digitized form of the signals 14 are placed inpredefined locations in the RAM 30 corresponding to predefined sensorpositions. The signals 14 corresponding to particular sensor positionscan alternatively or additionally be stored in secondary storage, suchas the disk storage unit 27 or the tape 29.

Once the signals 14 have been digitized and stored in the RAM 30, adetermination is made whether the apparatus 10 is in the EEG or the EPmode. If operating in the EEG mode the procedure skips to step B shownin FIG. 1BB. If, however, the apparatus 10 is in the EP mode, thesignals 14 are accumulated in the predefined locations in the RAM 30and/or can be stored in the disk storage unit 27 or the tape 29.Operation of the apparatus 10 then proceeds to determine whether theselected number of signals 14 have been acquired in accordance with theinitial setup parameters. If the selected number of the signals 14 hasbeen acquired in the appropriate manner, processing proceeds to step Bwhich continues in FIG. 1BB. If, however, the selected number of thesignals 14 has not been acquired, then processing resumes at the step ofapplying the predefined stimuli 16. This operation of the apparatus 10in the EP mode shown in FIG. 1BA continues until the selected number ofthe signals 14 have been acquired.

Referring to FIG. 1BB, the operation continues at step B from FIG. 1BA.At this point the RAM 30 contains data representative of theaccumulation of the digitized signals 14 at predefined locations in theRAM 30 corresponding to respective sensor positions. Alternatively atthis point, accumulated data signals can be input from a secondarystorage source, such as the disk storage unit 27, to the RAM 30 toprovide the initial database from which further manipulation proceeds.The next step in the operation is the selection of one of a plurality ofoptions as to how to operate on the signals 14. Once the option isselected, the apparatus 10 proceeds to perform the appropriateoperations on the signals 14 as stored and accumulated in the RAM 30.These operations on the signals 14 can include, for example, attenuationor amplification, digital filtering, smoothing, fast Fouriertransformation, differentiation, integration and statistical dataanalysis. In other forms of the invention these operations can beperformed prior to storage in the RAM 30, such as after the A/Dconversion 28 and prior to initial storage in the RAM 30.

After the selected option has been performed, the result of theoperation is stored again in the RAM 30, either at new locations or atthe previous locations, such as by overwriting the previous locationswith the new form of the signals 14. Alternatively or additionally, theresults can be stored in a secondary storage such as the disk storageunit 27. At this point, the signals 14 stored in the RAM 30 provide thebasis for interpolation, either line by line or in an interlaced oralternate line mode of output, and the interpolated form of the signals14 is output in a display format compatible with the DPU 39. The DPU 39therefore receives and stores the interpolated form of the signals 14 inthe display RAM of the DPU 39, one line at a time, as shown in the nextblock of FIG. 1BB. The DPU 39 generates an image on a display means,such as a video display 43 (for example, a Zenith ZVM-133), or the imageis output to another form of the display means, such as an ink jetprinter 45 (for example, a TRS 80 CGP220 manufactured by Tandy Corp.).

Interpolation

In the illustrated form of the invention, the input activity signals 14stored in the RAM 30 undergo an interpolation within the RAM 30 undercontrol of the microprocessor unit 22. An expanded matrix is formed offiner resolution (for example, a forty by forty array of points in thepreferred embodiment) than the arrangement of the twenty-one electrodesensors 12. The general technique of interpolation using three points toform finer resolution frames of the input activity signals 14 is known(see, for example, Duffy et al., "Brain Electrical Activity Mapping"referred to hereinbefore). However, as will be discussed hereinafter,the present invention includes an improved interpolation method whichuses a set of two points to generate and output line-by-line theinterpolated form of the input activity signals 14.

In the preferred embodiment, a line is one line of pixels, wherein apixel is the smallest picture element used to construct the video image.As will be described in more detail hereinafter, each pixel color isdescribed completely by three bits of digital information stored in theRAM 30. In alternative forms of the invention a color mapping procedurecan be used to assign color values to the pixels. For example, eachpixel can have five bits in the RAM 30 to describe one of thirty-twopossible color choices which points to a color map also located in theRAM 30. The color map can have a preselected number of n bits ofinformation which describes each of 2^(n) possible colors, and the colormap digital description is output to the intensity digital to analogconverter part of the DPU 39 for display of the desired pixel color.

Upon completion of the interpolation for a given line, the interpolatedvalues can also be stored in a disk storage unit 27 for future use andanalysis. A video output 37 of the interpolated input activity signals14 is output line-by-line to the DPU 39 (preferably contained within themicroprocessor unit 22 as discussed hereinbefore) in preparation foroutput to the video display 43. The interpolated form of the signals 14can also be output from the RAM 30 or the DPU 39 for hard copy printouton the printer 45 or for completion of an additional data analysis 40before being displayed. These alternative operations will be discussedin more detail hereinafter.

In the illustrated embodiments of FIG. 3 and FIGS. 4A and 4B, theinterpolation begins by generating amplitudes at four projectedelectrode sensors 31 at the corners of the matrix of the electrodesensors 12 to establish a rectangularly symmetric five by five matrix ofthe input activity signals 14. The values for the four signals 14 at theprojected electrode sensors 31 are interpolated from a linear averageprojection from the intersecting perpendicular lines of the electrodesensors 12 which converge on each of the projected electrode sensors 31.Once the signals 14 have been established at each of the projectedelectrode sensors 31, the interpolation proceeds by selecting a firstline, such as a line 33 in FIG. 3 along the perimeter of the matrix ofthe electrode sensors 12, and starting with line 33 the line-by-lineinterpolation is carried out parallel to the line 33.

The use of a commercial polygraph unit with, for example, twenty-one ofthe electrode sensors 12, rather than twenty-five actual sensors for thefive by five matrix, enables use of a standard unit of substantiallylower cost to the user. Further, the approximately rectangulararrangement for the twenty-one electrode sensors 12 enables theinterpolation procedure to be simplified. In one form of the inventiondescribed in FIG. 4B interpolation proceeds along lines which areparallel to one another and pass through the regular array of pointsdefined by the rectangular arrangement of the electrode sensors 12.Therefore, the interpolation takes place along one-dimensional lineswhich are easily defined in the rectangular arrangement andinterpolation calculations are performed more easily using only twopoints to generate a bracketed intermediate point. In prior conventionalinterpolation approaches, three points from a nonrectangular arrangementhave been used (see, for example, U.S. Pat. No. 4,417,591, which isincorporated by reference herein).

In a preferred form of the invention described in FIG. 4A, afterdetermination of the signals 14 at the projected electrode sensors 31,the linear interpolation is carried out for selected points apredetermined fraction of the distance between each nearest neighborpair of the signals 14 in a column 25 of the electrode sensors 12. Aninterpolated value for the selected point is determined by forming alinear weighted average of an appropriate pair of the input activitysignals 14. This pair is either two of the signals 14 selected from theelectrode sensors 12, or is one of the signals 14 at one of theelectrode sensors 12 and one of the projected sensors 31, which bracketthe location of the selected point. For example, in the illustratedembodiment of FIG. 3 the distance between each of the electrode sensors12 is divided into eight parts. Thus, if the selected point isone-eighth of the distance between a first one of the sensors 12 and asecond one of the sensors 12, then the value for the electrical activitysignal 14 at the interpolated point is seven-eighths the value of thesignal 14 at the first sensor 12 plus one-eighth the value of the signal14 at the second sensor 12. This interpolation procedure continuessequentially up each of the columns 25 of the electrode sensors 12 untilthe interpolation is complete for all five of the columns 25 which areperpendicular to the line 33. The interpolation is then performed forall remaining lines parallel to the line 33, proceeding incrementallyfrom line 33 to line 35 and to the other lines until completion.

In another form of the invention shown in FIG. 4B, after theinterpolation along the line 33 has been completed, the interpolationproceeds point by point for the line 35 and for each of the subsequentlines parallel to the line 33. This procedure is accomplished by firstdetermining the signal 14 at the selected point which is a predeterminedfraction of the distance between the electrode sensor 12 contained inthe line 33 and the nearest electrode sensor 12 in the same column 25.This process is completed for only a first point in each of the fivecolumns 25 of the electrode sensors 12. The resulting five points areshown in FIG. 3 as interpolated values 38 which lie at the intersectionsof the columns 25 and the line 35. These values 38 are then used tocomplete the interpolation along the line 35 in the same manner asdescribed above for the embodiment of FIG. 4A. Interpolated values 41are therefore constructed from a linear weighted combination of theappropriate pair of the interpolated values 38 which bracket each of thevalues 41. The line 35 is then output for presentation on the videodisplay 43. The outputted form of the signals 14 comprising the line 35are therefore generated in a compatible format for the conventionalvideo display 43. Further details of operation of the video display 43can be obtained by reference to the Zenith ZVM-133 operating manual,which is incorporated by reference herein. Alternatively, the line 35 isoutput for the additional data analysis 40 prior to display, dependingon the user selected operational mode. Display of the complete frame ofa topographical map 44 shown in FIGS. 5 and 7 continues line-by-line,incrementally completing the interpolation for each of a plurality oflines and outputting each of the lines to the video display 43.

These interpolation procedures enable the live time line-by-lineprocessing of the input activity signals 14 for output to the videodisplay 43. The live time output and display of the signals 14 isaccomplished without having to await formation of the entire video frameand also without having to store in the RAM 30 a plurality of the linesor a complete frame of the input activity signals 14 before output tothe video display 43. Prior "live time"0 methods have required storageof the complete frame before the topographical map 44 could be displayed(see, for example, U.S. Pat. No. 4,417,591, which is incorporated byreference herein). Further, as mentioned hereinbefore, the presentline-by-line interpolation requires only two end points to perform theprocedure, and this greatly simplifies the calculation and storage ofvalues in the RAM 30 and decreases the calculation and display time.

In some forms of the invention, the input activity signals 14 undergoother operations prior to the data interpolation, such as the dataanalysis 40 (for example, data smoothing and a digital filteringtreatment to be discussed in more detail hereinafter). Another exampleof the data analysis 40 is the performance of a Fourier transformationof the EEG form of the input activity signals 14 from the twenty-oneelectrode sensors 12. In order to avoid performing time consumingFourier transformation for the larger number of values in the expandedframe containing the interpolated values 38 and 41, only the smallnumbers (twenty-one in the illustrated embodiment) of the unexpandedinput activity signals 14 undergo Fourier transformation. Interpolationexpansion to a finer matrix is generally done more efficiently on thedata after completion of any extensive or complicated form of signaltreatment, such as the Fourier transformation operation.

Video Display

In the preferred embodiment, after the interpolation and the optionaldata analysis 40 of the input activity signals 14, the resulting videooutput 37 is applied to the DPU 39 contained in the Zenith Z-100 unitAlternatively, the raw input activity signals 14 accumulated in the RAM30 can be output as a raw signal 25 by the microprocessor unit 22 to theDPU 39 without further processing, including interpolation. The videooutput 37 input to the DPU 39 is converted into an output signal 47suitable for the video display 43 which provides the topographical map44.

In the preferred embodiment there is one display rate, other thanmanually sequencing through the set of frames, for dynamic display ofthe change in EP response as a function of time elapsed after thestimulus 16 has been applied to the patient's head 13. The display ratecan also be increased by generating reduced sizes of the topographicalmaps 44, in a manner to be described in detail hereinafter. Operation ofa typical form of the DPU 39 has been discussed hereinbefore in theInterpolation section and is also explained in, "Fundamentals ofComputer Graphics," J. D. Foley and A. Van Dam, Addison-Wesley Co.,Reading, Mass., 1982, pp. 112-136, which is incorporated by referenceherein. Also, see U.S. Pat. Nos. 4,121,283, 4,139,838 and 4,213,189which are incorporated by reference herein.

In addition to the generation of the video display 43, as mentionedhereinbefore the interpolated input activity signals 14 are selectivelystored in the disk storage unit 27 or applied to the ink jet printer 45which provides a hard copy printout of the topographical map 44. Theuser selects print out of the topographical map 44 on the video display43 by actuating transfer of the video output 47 to a page buffer 49coupled to the ink jet printer 45. Upon filling the page buffer 49, theprinter 45 outputs the hard copy printout.

In the illustrated embodiment of FIG. 5, the topographical map 44 iscolor coded, and in a preferred form of the invention thirty-twodifferent color choices are used to encode the relative magnitude of thebrain electrical activity for the input activity signals 14 displayed onthe topographical map 44. In the illustrated embodiment of FIGS. 1 and5, color code means for encoding the colors on the topographical map 44is accomplished in conjunction with a software program which is readinto the RAM 30 from the disk 29. The topographical map 44 isconstructed of blocks of two by four, or eight, pixels; and as mentionedhereinbefore each of the pixels in the block are described by threeseparate storage bits, one for each of the memory locations in the RAM30 associated with the red, green and blue colors which are used toconstruct all the colors. With three storage bits per pixel a total oftwo cubed, or eight, unique colors can be constructed. These eightcolors, along with white, are assigned to individual pixels in the blockand are mixed to generate twenty-four more colors. For example, theblock of two by four pixels can be constructed in a predetermined mannerusing the unique colors to arrange the colors of near neighbor pixelsaround a selected given pixel to form a block having a light yellowappearance. This is accomplished by having every next nearest neighborpixel of the selected given pixel as a yellow pixel, which is describedby the green storage bit as "1", the red bit as "0" and the blue bit as"1". The remaining nearest neighbor pixels around the given pixel arewhite with the red, green and blue storage bits all "1". Colors for thepixel blocks other than the unique colors are constructed in a similarfashion by mixing two preselected colors in the pixel blocks in theabove described manner. This method of color construction further helpsto reduce the cost of the apparatus 10 which substantially enhances thecommercial significance and usefulness of the apparatus 10.

In the illustrated embodiment the color coding of the topographical map44 is graphically explained to the user by generating alongside the map44 a vertically positioned, color column or scale 46 having differentcolor segments 48. The thirty-two colors in the illustrated embodimentare depicted by various cross hatching and line patterns. Each of thecolor segments 48 represents a fixed relative magnitude within aselected closed data set of the interpolated values 38 and 41 for theinput activity signals 14. A closed data set is meant to include thoseinput activity signals 14 measured on the patient's head 13 for a fixedset of measurement variables, such as, amplifier gain and the nature ofthe stimulus 16.

In alternative forms of the invention, the color scale 46 is positionedhorizontally or is arranged alongside selected portions of any number ofsides (for example, four if rectangular) of the topographical map 44.The user can also select the display of only the color segments 48 whichare being displayed on the associated topographical map 44. This enablesremoval of unused colors to simplify association of colors with anamplitude at a selected location on the topographical maps 44.

In the illustrated embodiment of FIG. 5 in addition to the topographicalmap 44 and the color scale 46, the video display 43 also includeswaveforms 50 which are characteristic of the EP response input activitysignal 14 at the user selected electrode sensors 12. The user also candisplay the waveforms 50 associated with the interpolated values 38 and41. Each of the waveforms 50 is output and displayed as a color codedline and also is identified using a conventional international formatwith an appropriate letter and number (for example, CZ, O1 and F7 inFIG. 5). The letter and number are indicative of the selected electrodesensor 12 or other interpolated point, such as one of the interpolatedvalues 38 or 41.

In FIG. 5 are shown examples of the waveform 50 for EP responseamplitudes which vary as a function of time above and below a centeredzero base line. Typically, the EP response is measured over time periodsof 256, 512, 1024 or 2048 milliseconds. The topographical maps 44 appearto the viewer as a series of frames showing the outline of the patient'shead 13. Each of the frames is characteristic of the EP responseamplitudes at a particular time after applying the stimulus 16 to thepatient. For example, each frame can represent one particular fourmillisecond time segment of the total set of the frames which covers thetime period from zero to 512 milliseconds in four millisecondincrements. Therefore, for each of the user selected locations on thepatient's head 13 for one of the frames, there is displayed theassociated waveform 50. A particular point on the waveform 50 describesthe amplitude for a particular time segment after the stimulus 16 hasbeen applied to the patient. In order to pinpoint the time segment onthe waveform 50, an indicator or a cursor 52 is displayed in FIG. 5which points toward the time segment and to the amplitude on thewaveform 50.

In the display of the topographical maps 44 of the EEG input activitysignals 14 the user is able to select one of the locations (such as, atone of the sensors 12 or the interpolated values 38 or 41) on thepatient's head 13 and generate adjacent the EEG topographical maps 44 anEEG curve of the contribution from the various frequency bands (i.e., α,β, δ and θ). The curve amplitude is correlated to an associated one ofthe frequency bands by using color coded segments positioned along theabscissa, or frequency, axis of the EEG curve. The color coded segmentis indicative of preselected ones of the frequency bands, such as the α,β, δ and θ bands.

The user of the apparatus 10 also has the ability to select the displayof a plurality of reduced sizes of the topographical maps 44. Thisfeature enables the user to display a number of the topographical maps44 on a single screen of the video display 43 or a single page of aprinted output. For example, in FIG. 7 is illustrated the display of aplurality of the topographical maps 44, along with the color scale 46.In alternative forms of the invention the user also displays thewaveforms 50 for the same or for different locations in each of theplurality of the topographical maps 44. The user can also select todisplay different brain electrical activity states or different types ofmeasurements for the reduced size topographical maps 44. For example,the user can select the display of EP responses and EEG information orEP responses characteristic of a plurality of different ones of thestimuli 16.

COMPUTER SOFTWARE

The apparatus 10 performs an analysis of the input activity signals 14to provide the video output 37 responsive to various means, such as forexample, computer means. In the illustrated embodiment of FIG. 1 thecomputer means comprises a computer software program selected by theuser and the microprocessor unit 22 which executes the software program.In a preferred form of the invention shown in FIG. 1, the computerprograms are stored on the disk or tape 29 and are loaded into the RAM30 in preparation for execution by the microprocessor unit 22. In otherforms of the invention, the computer programs of the computer means areinput or downloaded from an external source, such as a remote softwarestorage location (not shown) or a remote computer 53, into the RAM 30 inpreparation for execution in the microprocessor unit 22. Alternatively,the computer programs are input directly into the microprocessor unit 22for execution therein. The means for providing the video output 37 alsocan generally include any form of logic means, hardware and software,which performs an analysis responsive to computer software programs toanalyze the amplified and digitized input activity signals 14 togenerate the video output 37.

When the apparatus 10 processes data from a remote means, such as aremotely located polygraph or an electrode sensor 12 for sensing thesignals 14, the signals 14 are input to an interface means (not shown).This interface means translates the signals 14 to enable communicationby a modem over a telephone line or other suitable telecommunicationsequipment to the processing means and to logic or computer means foranalysis to generate the video output 47. Such a form of the apparatus10 avoids the need to have a dedicated system and makes feasible themeasurement of the signals 14 at remote locations and enables theclinical use of the apparatus 10 by clinics and practioners who wouldotherwise be unable to support a dedicated system.

In the preferred embodiment, a master control program is provided as anexecutive which guides the user through the necessary steps for initialcalibration of the apparatus 10, setting of apparatus parameters,including type of functions desired, topographical and Fourier transformdata, filter characteristics, number of samples per second, displayupdate frequency and so forth. The user calls up the executive programwhich then sequences the user through the appropriate command requeststo provide for various functionality as described throughout thisspecification. The executive can be written in any plurality oflanguages, including assembly language, BASIC, FORTRAN, etc., and canoperate under a plurality of commercially available operating systems,such as CP/M-86, MS-DOS or UNIX, on any of the plurality of commercialsystems, such as the Zenith Z-100 system given as an examplehereinbefore.

Once the apparatus 10 is calibrated and necessary set-up data isprovided, the apparatus 10 can provide the topographical map 44 of thebrain electrical activity in either live time, as sampled data is beingacquired and stored, or mapping and display of the brain electricalactivity can be performed on prestored or transferred data files notactually gathered in live time and can even be performed at an external,remote location relative to the apparatus 10. The mapping and displayoperation can be performed by the apparatus 10 and/or electronichardware processing of the input activity signals 14. Hard copy printouton the printer 45 and/or output to the video display 43 can be providedat the user's selection.

In another form of the invention instead of the master control program,the apparatus 10 can provide all necessary functions by providing aplurality of separate callable software routines for the user to call upat his option. In this case, no central executive program would berequired.

The software programs are utilized in certain selected modes ofmeasurement and analysis, while other programs are utilized in all modesof measurement and analysis of brain electrical activity. These computersoftware programs are explained in the subsections describedhereinbelow:

Digital Filtering

The digital filtering program is one form of an analyzer means whichmore particularly acts as a filter means, such as a digital filter 54shown in FIG. 1. In selected areas of biological science the concept ofdigital filtering is a conventional method for removing or attenuatingunwanted signals (see, for example, A. R. Moller, "Improving Brain StemAuditory Evoked Potential Recordings by Digital Filtering," Ear andHearing 2, 108-113 (1983); and A. V. Oppenheim et al., Digital SignalProcessing, chap. 5, Prentice-Hall, Englewood Cliffs, N.J. 1975; whichare incorporated by reference herein). In the present invention the useris able to attenuate or substantially remove unwanted extraneous signalsfrom the input activity signals 14 by applying a digitized filterfunction thereto. The digitized filter function is loaded in the RAM 30from the disk or tape 29 or from the remote computer 53. The digitizedfilter function is stored as attenuation (dB) in digitized form in theRAM 30 with an eight bit segment of the RAM 30 containing theattenuation value for one particular associated frequency. A completefrequency range for the digitized filter function is therefore embodiedwithin a plurality of eight bit storage segments located in the RAM 30.More or less numbers of the segments can be utilized for more or lessresolution of the frequency range. In performing the filtering operationthe stored attenuation factors are applied to the stored amplitude atthe associated frequencies to provide the reduced forms of the inputactivity signals 14.

In a conventional system a hardware based filter is usually appliedbefore the signal 14 is digitized. Thus, the hardware filter is normallypositioned immediately after the input activity signal 14 is output fromthe amplifier 26. However, in addition to attenuating unwanted signals,there is also some attenuation outside the optimum frequency range dueto an inherent lack of a sharp cutoff in the attenuation for thehardware based filters. Further, the conventional hardware filter causesshifts in signal phase which distort the shape and position of the inputactivity signals 14. The digital filter 54 is however programmable tohave a sharp cutoff and not introduce signal phase shifts when appliedto the input activity signal 14. Nevertheless, where appropriate filtercharacteristics are achievable, the hardware filter could be utilized.

In the preferred form of the invention, the apparatus 10 uses thedigital filter 54 derived from computer system hardware and software ofthe apparatus 10. Digital filtering is provided by the digital filter 54responsive to the input activity signal 14 for locations after theaccumulated averaged form of the signal 14 has been stored in the RAM30, but before the interpolation has been performed. In other forms ofthe invention, the digital filter 54 is applied immediately after theinput activity signal 14 is output from the multiplexer 24 (see FIG. 1)or after output from the A/D converter 28. Alternatively, the digitalfilter 54 is applied after the interpolated form of the input activitysignal 14 has been generated.

In the illustrated embodiment, the digital filter 54 is applied afterstorage of the input activity signals 14 in the RAM 30. The originalmeasured form of the input activity signal 14 is retained in unchangedform in the RAM 30; and therefore, the digital filter 54 can be changedand applied repeatedly to the input activity signal 14 in the process ofthe user analyzing the signal 14. The digital filter 54 is readilymodified by user programming, and consequently the user has greatversatility in constructing virtually any combination of low or highpass or band pass filter necessary to analyze the input activity signal14.

Noise Evaluation

The evaluation of a noise signal often enables the user to compensatefor the noise by utilizing an electronic filter, such as the digitalfilter 54, to attenuate the noise signal to provide a reduced, orsubstantially noise-free, form of the input activity signal 14 for moremeaningful data analysis. Alternatively, if the user can identify thesource of the noise signal, the noise source might be eliminatedaltogether. Noise identification and attenuation or reduction is knownin selected areas of biological science (see, for example, Introductionto Automated Arrhythmia Detection, ch.5, K. L. Ripley and A. Murray,IEEE Computer Society, No. EH 0171.9,1980; and see R. H. Wong and R. G.Bickford, "Brainstem Auditory Evoked Potentials: The Use of NoiseEstimates," Electroencephelography 50, 35-34, (1980); which areincorporated by reference herein).

Another aspect of the analyzer means is noise evaluation alone which iscarried out by the apparatus 10 responsive to software programs directedto determination of the noise signals. Knowing the noise signalbehavior, the user can often program the digital filter 54 to attenuatethe noise signal. One type of noise evaluation program is directed toevaluation of noise signals which do not have long term, constantfrequency and amplitude. This type of noise evaluation is directed to,for example, noise signals comprising random noise, spurious occasionalcomponents of irregular frequency and varying amplitude and spurioustemporary components of regular frequency noise.

FIG. 6 illustrates one embodiment of the invention used for isolation ofextraneous noise signals present in the measurement of brain electricalactivity signals. The converted input activity signal 14 output from theA/D converter 28 is input to multiplexer means, such as a multiplexer56, which distributes and accumulates the activity signal 14 in at leasttwo alternate memory locations, a first memory 57 and a second memory58. The signal 14 is entered into these locations by alternating dataentry between the memory locations 57 and 58. If the noise signal israndom noise or is a continuous but irregular frequency signal, thenoise signal is characterizable by applying subtraction means togenerate a subtracted output of the arithmetic difference between theinput activity signals 14 in the first memory location 57 and the inputactivity signals 14 in the second memory location 58. Knowing the noisesignal, the user can selectively attenuate this unwanted noise signalusing filters, such as the digital filter 54. If, however, the noisesignal happens to be similar in frequency to the input activity signal14, the filtration is more difficult. In such cases the user might haveto eliminate the source of the noise signal or alter experimentalconditions to distinguish and attenuate the noise signal.

The nature of the noise signal to be evaluated also affects the analysisprocedure, such as the number of values of the signal 14 to be enteredin each of the memory locations 57 or 58 before switching data entry tothe other memory location 57 or 58. For evaluating random noise signals,it is acceptable to enter every odd numbered data signal in the firstmemory location 57 and every even numbered data signal in the secondmemory location 58. For example, when measuring EP response curves,every other set of values which constitute the EP response to thestimulus 16 is accumulated in the first memory location 57 and the othersets of responses are accumulated in the location 58.

When the noise spectrum takes other forms, such as a spurious noiseburst of irregular frequency and amplitude, correct analysis of thenoise signal depends on having a substantial portion of the noise signalisolated within one segment (or other identifiable portion) of one ofthe memory locations 57 or 58. If the noise signal is evenly distributedin the memory locations 56 and 58, this method does not enable one toreadily distinguish the noise signal portion. Therefore, in general,data is stored and accumulated in one of a plurality of memory locationswith a user selectable time period for accumulating data in each of thememory locations before switching to another of the memory locations.For example, ten entries of the signal 14 can be stored in one of aplurality of memory locations before switching to the next memorylocation for the next ten entries of the signal 14. Accordingly, theuser should determine by independent analysis the expected varieties ofnoise and select the number of data entries and time period foraccumulation in each of the memory locations. In this manner, noisesignals which have a particular time duration can be isolated. Afterdetermination of the noise signal and of the noise corrected form of theinput activity signal 14, the user can also evaluate the noise signal bycalculation of a signal to noise ratio which assists in evaluating thenature and magnitude of the noise signal and provides a way to evaluatethe quality of the experimental conditions.

In another form of the invention the apparatus 10 responsive to analyzermeans in the form of a software program evaluates the noise signal byperforming a Fourier transformation to isolate the frequency componentsassociated with the noise signal. The Fourier transformation ispreferably carried out as a fast Fourier transformation procedure in aconventional manner as indicated hereinafter. Once the noise signal hasbeen evaluated, the digital filter 54 is programmed to attenuate theknown noise signal. This Fourier transformation analysis can also bepreceded or followed by one of the previously discussed procedures foranalyzing the noise signals.

Statistical Analysis

Statistical evaluation of an individual patient's characteristictopographical map of brain electrical activity is accomplished by suchconventional approaches as z-statistics and t-statistics (see, forexample, U.S. Pat. Nos. 4,201,224 (John) and 3,780,724 (John) which areincorporated by reference herein). For example, in the case ofz-statistics, the patient response in terms of the input activitysignals 14 at each of the points of the topographical map 44 isexpressed in terms of the number of standard deviations from the averageresponse of a group of a representative normal population.

Fourier Transformation

The apparatus 10 responsive to a software program carries out a Fouriertransformation analysis of the frequency energy components in an EEGmeasurement. As mentioned hereinbefore, a conventional fast Fouriertransformation (FFT) is preferably used to carry out the transformationof the signals 14. The FFT is explained by Oppenheim et al., DigitalSignal Processing, ch. 6, Prentice-Hall, Englewood Cliffs, N.J., 1975,which is incorporated by reference herein.

The EEG input activity signals 14 are sampled at predetermined timeintervals, approximately 2.5 second segments, to provide a selectabletotal number of 256 to 2048 segments of the sampled form of the EEGinput activity signals 14 (see, for example, Ueno et al., "TopographicComputer Display of Abnormal EEG Activities in Patients with CNSDiseases," Memoirs of the Faculty of Engineering, Kyushu University,Volume 34, February, 1975, pages 195-209; which is incorporated byreference herein). In the illustrated embodiment sampling means forobtaining the signal samples takes the form of a software program in thedisk 29 and is executed by the microprocessor unit 22. The softwareprogram actuates measurement of the signals 14 at the predetermined timeintervals in accordance with a timing routine. The output from theFourier transformation analysis of the segments of the input activitysignal 14 enables determination of the frequency band energy outputpresent in at least the major EEG frequency bands of α, β, δ and θ. Inanother form of the invention other subintervals of some of these bandsare also evaluated. The frequency band energy outputs can be furtheranalyzed by one of the statistical analysis software programs and/or thenoise evaluation programs. The frequency band energy outputs are thenprocessed by the DPU 39, and the video display 43 generates theappropriate topographical map 44.

Threshold Activation

In some modes of data acquisition, it is desirable not to enable, oractuate, accumulation and analysis of data unless the incoming inputactivity signals 14 attain or exceed a predetermined condition, such asa predetermined threshold amplitude or frequency level. This approachallows particular classes of data to be analyzed without superfluousdata being present. For example, epileptic spikes occur intermittentlyand generate a large amplitude spike.

After a preliminary screening of the patient, threshold activationprogram data in the form of the predetermined condition is establishedand is placed by the input means (such as the keyboard 23 or the disk29) into the RAM 30 or into separate hardware means for storing andtesting the predetermined condition such as threshold test circuitry 55shown in FIG. 1. The microprocessor unit 22 uses the predeterminedcondition stored in the RAM 30, or embodied within the circuitry 55, tocompare with the incoming input activity signals 14. Therefore, theinput activity signals 14 are stored and analyzed by the apparatus 10only if the signal amplitude exceeds the predetermined condition.

In an alternative form of the invention the apparatus 10, responsive toa software program, carries out a differentiation of the incoming inputactivity signal 14, and when the amplitude of the differentiated signalexceeds the predetermined condition, the apparatus 10 accumulates andanalyzes the signal 14. In this manner the onset of a sharp spike, suchas an epileptic spike having a rapidly changing curve slope, isdetected, and the spike subsequently undergoes analysis.

In another form of the invention the apparatus 10, responsive to thethreshold activation program data, detects and analyzes a predeterminedthreshold frequency level by employing frequency means in the form ofconventional frequency counting circuitry (see, for example,"Electronics for Scientists and Engineers", Prentice Hall, EnglewoodCliffs, N.J., 1967, pages 321-322 and 470-473, which is incorporated byreference herein). The output from the frequency counting circuit is asignal whose amplitude is proportional to the frequency detected;therefore, the predetermined condition for the threshold frequency levelis set to actuate data acquisition and analysis of the incoming inputactivity signal 14 whenever the predetermined frequency level has beenexceeded.

In another aspect of the invention the apparatus 10 measures the numberof zero crossing events (a form of frequency determination) and datataking is activated upon exceeding a predetermined number of suchevents. The microprocessor unit 22 or the test circuitry 55 evaluatesthe algebraic sign for each one of the input activity signals 14 andmaintains a running count of the number of changes in the algebraic signwithin a given time period. When the number of algebraic sign changeswithin the given time period exceeds a predetermined number, dataaccumulation and analysis is activated, and the resulting input activitysignals 14 are displayed as the topographical maps 44.

The apparatus 10 responsive to the threshold activation program is ableto actuate analysis of any of the input activity signals 14 wherein theuser wishes to restrict analysis, for examle, to a large amplitudesignal, to a high frequency signal or to other selected distinguishablefeatures Advantages of the threshold activation program include use ofless overall storage area in memory for analysis of the signals 14,performance of more detailed data analysis in a given time period ofactual calculation by the microprocessor and faster and more efficientanalysis of a complete data set compared to the case of analyzing allincoming data.

Integration, Differentiation and Difference Measurements

The apparatus 10 responsive to an integration software program operateson frames of the input activity signals 14 measured for EP responses tocharacterize the time integrated response output. This integrated outputenables an evaluation of spatial locations on the patient's head 13and/or the time segments of the EP response which make the mostimportant contributions to the input activity signals 14. Integration iscarried out over a range of user selected time segments, and in FIG. 7the integrated output for some of the selectable time segments isdisplayed in the resulting topographical maps 44. The integrated outputof the input activity signals 14 of the topographical maps 44 results incombining a number of separate smaller time period segments of the inputactivity signals 14. Therefore, the user views in a small number of thetopographical maps 44 the behavior of the input activity signals 14 overa broad time range. The time range of 0 to 240 milliseconds is shown inonly six frames of integrated EP response. Such a display mode istherefore beneficial to the user to carry on an evaluation of a largeamount of data without requiring separate display of a large number ofthe topographical maps 44 and without having to switch between a largenumber of the topographical maps 44.

The apparatus 10 responsive to a differentiation software programoperates on frames of the input activity signals 14 from EP responses tocharacterize the first or second order differential of the EP responses.This differential response enables an evaluation of locations of thetime segments which contain the most significant contributions tochanges (first order) and rate of change (second order) in the amplitudewith respect to location and time of the EP response curves. The usercan select the spatial location and/or the time interval over which thedifferentiation is calculated. The analysis enables spatial and timeanalysis of rapidly changing EP responses which supplements informationobtained from the integration output. The analysis can also be carriedout for changes and rate of change in amplitude with respect to locationfor the EEG input activity signals 14.

The apparatus 10 is also responsive to a difference software programwhich operates on frames of the input activity signals 14 from the EPresponses to evaluate the arithmetic difference from one of the userselected frames to another, each of the frames characteristic of apreselected time after application of the stimulus 16.

Montage Analysis

The apparatus 10 responsive to a computer montage analysis programcarries out a difference type of analysis of the input activity signals14 to isolate and identify features of interest, such as epilepticspikes. The analysis is accomplished by selecting one or more of theelectrode sensors 12 as reference electrodes with the rest of theelectrode sensors 12 having the role of active electrode sensors 12. Themontage analysis is performed by using the input activity signals 14stored in memory means, such as the RAM 30, and thus repeated actualmeasurements are unnecessary. In a preferred form of the invention thetwenty-one electrode sensors in FIG. 1 are assigned active roles and anadditional electrode sensor 12 is attached near the patient's ear to actas the reference electrode sensor 12. The difference form of the inputactivity signal 14 is calculated, and the values are stored in the RAM30. The user then views the difference signals 14 and determines theapproximate location of the feature of interest. The user next selects anew one of the reference electrode sensor 12 and active electrodesensors 12 which are in close proximity to the feature of interest. Thedifference form of the input activity signals 14 are calculated, and thelocation and appearance of the feature of interest is isolated withgreater precision. This iteration continues by recycling back to theselection of new ones of the reference and active electrode sensors 12until completion of the identification of the feature of interest

In other forms of the invention for each selected set of the referenceand active electrode sensors 12, an average value can be calculated foreach set of the sensors 12 in every frame of the input activity signals14. These average values are then subtracted from one another to formthe difference form of the signals 14. For example, if the feature ofinterest is a sharp peak extending along a line, the user could selectten of the sensors on one side of the distended peak as referenceelectrodes and eleven on the other side as active electrodes. Theaverage of each set is then subtracted from the average of the other foreach of the frames. The difference form of the input activity signals 14is then calculated for a selected number of the frames, (for example,the user can select from the 240 frames for measurements of the EPresponse taken every four milliseconds from 0 to 960 milliseconds afterthe application of the stimulus 16). As discussed hereinabove, thisiterative analysis procedure can be repeated using recycle means toreturn to the beginning of the montage iterative analysis procedure byselecting a different set of the electrode sensors 12 as the referenceelectrode sensor 12. This iterative process is continued until thesource of any feature of interest, such as the above mentioned distendedtype of peak, is identified or isolated. This procedure can beprogrammed to iterate automatically to a solution, or the user caninteract to select various combinations of active and referenceelectrode sensors 12 to locate the most prominent features. Therefore,the recycle means can be a user signal to return to perform anotheriterative analysis or can be an interrupt and branching command in thesoftware program to automatically recycle until the specified feature isidentified in accordance with predetermined conditions stored in the RAM30. The resulting set of difference input activity signals are stored inthe RAM 30 at locations different from the input activity signals 14 andare compared to one another. These difference input activity signals 14can also undergo the additional analysis 40 and provide other forms ofthe topographical maps 44 of EP response and EEG measurements. Displayof the difference signals 14 and their derivatives from the analysis 40enable diagnosis of disparities associated with brain abnormalities.

Montage analysis has important advantages over the prior art because theinstant approach uses only one set of the measured input activitysignals 14 which are stored in the RAM 30. Conventional methods,however, require repeated measurements since the montage analysisproceeds by selecting a first set of one or more reference electrodesensors 12, measuring a set of signals for the remainder of theplurality of the electrode sensors 12, computing and recording thedifference of the signals 14, establishing a new set of referenceelectrode sensors 12 and measuring a new set of differences in thesignals 14. This procedure is sequentially repeated until the locationof the feature of interest has been isolated. The computer programmontage analysis renders unnecessary this time consuming and repetitivetask and substantially reduces the time for data taking and analysis.

Cognitive Test Mode

The apparatus 10 responsive to a cognitive testing software programeffectuates tests of recognition ability which enables diagnosis of anumber of abnormalities (see, for example, U.S. Pat. No. 3,901,215(John) which is incorporated by reference herein). The instant cognitivetesting program makes full use of a period of data acquisition bysorting the responses to different types of the stimuli 16 intodifferent memory locations of the RAM 30. Ordinarily cognitive testingis accomplished by acquiring the input activity signals 14 for aplurality of completely different time periods, wherein each time periodis devoted solely to either a regular form of the stimulus 16 andresponse thereto or to an intermittent form of the stimulus 16 andassociated response. Examples of the different types of the stimuli 16can include a mixture of different amplitude audible tones, tones ofdifferent frequency and a tone pattern with intermittent absences ofcertain anticipated tones.

The microprocessor unit 22 controls administration of the predeterminedpattern of the stimulus 16 during the cognitive testing mode ofoperation responsive to the cognitive test software, and therefore themicroprocessor unit 22 flags each of the applied stimuli 16. Epending onthe nature of the stimulus 16 the flagging enables the microprocessor 22to sort the resulting EP responses comprised of a set of the inputactivity signals 14 associated with each type of the stimulus 16, intothe different memory locations. Comparison and analysis, such asstatistical analysis, is then performed on the signals 14 stored in thedifferent memory locations. This procedure therefore makes datacollection more efficient and reduces the time to collect sufficientdata characteristic of the input activity signals 14.

Video Display and Interaction Modes

The apparatus 10 responsive to an interlace software program results inthe interpolation and the output to the display memory of the DPU 39 ofevery other pixel line in one frame to the video display 43. Uponcompletion of display of every other pixel line in a first completeframe or first topographical map 44, the program causes return of theraster beam to the beginning of the display cycle to perform alternatepixel line interpolation and display in the next frame, or the nexttopographical map 44, of the set of pixel lines skipped in the firstdisplay cycle. By virtue of having to process and display only everyother pixel line of the input activity signals 14, the interlace modeenables an apparent increase in display speed by updating at, forexample, twelve frames/second the display memory of the DPU 39. Thevideo display 43 therefore generates a plurality of the topographicalmaps 44 at an apparent rate of nearly twenty-four frames/second becausein each frame every other pixel line is displayed. This results in asmooth cartooning effect without apparent loss of resolution to thehuman eye.

In the interaction modes the mouse 36 or the light pen 34 are preferablyused as indicator means. The user generates an input signal so as tointeract with the information present on the video display 43 therebyactuating selected software programs. In the case of the mouse 34, thisuse takes the form of displaying a variety of selectable routines on thevideo display 43, moving a cursor to point to a designated label for oneof the routines and carrying out the routine by actuating a switch (notshown) on the mouse 36. Similarly, for the light pen 34, the user pointsto a location on the video display 43, and a screen sensor (not shown)detects the site of the light pen light spot and generates an activationoutput to the microprocessor unit 22 to actuate the appropriate softwareprogram. The software program also displays additional informationrelevant to the displayed topographic map 44, or further calculationscan be performed and displayed. For example, the user is able toselectively display the evoked potential waveforms 50 (illustrated inFIG. 5) for those points on the topographic map 44 designated by themouse 34 or by the light pen 34.

In another form of the invention, the apparatus 10 responsive to aninteraction means in the form of a software program can generate theamplitude of input activity signal contours along any indicated line onthe topographical map 44, the line being selected by the cursor of themouse 36 or by the light pen 34. Further, the software program can actas a map magnifying means by allowing the user to utilize the mouse 36or the light pen 34 to select an outline of an area of the topographicalmap 44 and expand the delineated portion to fill a selected portion ofthe video display 43.

While preferred embodiments of the present invention have beenillustrated and described, it will be understood that changes andmodifications can be made without departing from the invention in thebroader aspects. Various features of the invention are set forth in thefollowing claims.

What is claimed is:
 1. An apparatus for displaying a topographical mapof brain electrical acitivity of a patient, comprising:sensor meansdisposed on a patient's head for providing changeable amplitude signinput activity signals responsive to said brain electrical activity;processing means responsive to said changeable amplitude sign inputactivity signals for providing an amplified and digitized form of saidinput activity signals; means for providing a video output responsive tosaid amplified and digitized input activity signals, said video outputincluidng a set of interpolated input activity signals for positionsbetween the locations of said sensor means with said positions includingselected locations along at least two interpolated lines generatedbetween adjacent pairs of lines formed by connecting the locations ofsaid sensor means and at least two of said interpolated lines betweeneach said adjacent pairs of lines being generated from distinguishableappropriate combinations of said input activity signals, saidinterpolated input activity signals generated line--by--line anddisplayed while a next successive adjacent line for display is beinggenerated; and means for displaying said topographical map of said brainelectrical activity responsive to said video output.
 2. The apparatus asdefined in claim 1 wherein said sensor means comprises a plurality ofelectrode sensors.
 3. The apparatus as defined in claim 1 wherein saidset of interpolated input activity signals are generated from linearweighted appropriate pairs of said amplified and digitized inputactivity signals.
 4. The apparatus as defined in claim 1 furthercomprising means for providing statistically averaged values for saidinput activity signals responsive to said amplified and digitized inputactivity signals.
 5. The apparatus as defined in claim 4 wherein saidmeans for providing averaged values comprises a computer having a randomaccess memory.
 6. The apparatus as defined in claim 1 further includingcolor code means for displaying alongside said topographical maps apredetermined set of colors displayable on said topographical maps, eachof said colors representing an associated fixed relative value within aselected closed data set of said input activity signals.
 7. Theapparatus as defined in claim 6 wherein said color code means alongsideeach said topographical map includes at least said colors beingdisplayed on each said topographical map associated with said color codemeans.
 8. The apparatus as defined in claim 1 wherein said means fordisplaying includes a display processing unit having a display memorywhich is updated for display of selected ones of said lines of saidtopographical maps responsive to said input activity signal.
 9. Theapparatus as defined in claim 1 wherein said topographic maps areconstructed from pixels having a plurality of distinguishable colors,wherein each of said colors is selectively comprised of one unique colorand of at least two unique colors mixed in a predetermined manner amongnear neighbors of said pixels.
 10. An apparatus for displaying atopographical map of brain electrical activity sensed by a plurality ofelectrode sensors disposed on a patient's head, wherein said electrodesensors provide an associated plurality of input activity signals, saidapparatus comprising:processing means for providing an amplified anddigitized form of said plurality of input activity signals; computermeans for providing a video output responsive to said plurality ofamplified and digitized input activity signals, said video outputincluding a set of interpolated input activity signals for positionsbetween the locations of said electrode sensors with said positionsincluding selected locations along at least two interpolated linesgenerated between adjacent pairs of lines formed by connecting thelocations of said electrode sensors and at least two of saidinterpolated lines between each said adjacent pairs of lines beinggenerated from distinguishable appropriate combinations of said inputactivity signals; means for displaying said topographical maps of saidbrain electrical activity responsive to said video output; and colorcode means for displaying near each of said topographical maps apredetermined set of colors displayable on an associated one of saidtopographical maps, each of said colors representing an associated fixedrelative value within a selected closed data set of said input activitysignals.
 11. The apparatus as in claim 10 further characterized in thatsaid interpolated input activity signals have changeable amplitude signand are generated line--by--line, wherein display of each line isprovided while a next successive adjacent line for display is beinggenerated.
 12. The apparatus as defined in claim 10 wherein saidpredetermined set of colors is positionable along a portion of saidtopographical map.
 13. The apparatus as defined in claim 10 wherein saidpredetermined set of colors is positionable on the display along atleast one of a vertical scale and a horizontal scale.
 14. The apparatusas defined in claim 10 further including indicator means responsive to auser input for supplying an input signal for actuating selected softwareprograms to control said video output on said display means.
 15. Theapparatus as defined in claim 14 further comprising map magnifying meansresponsive to said input signal for selectively enlarging apredetermined portion of said topographical map for display.
 16. Anapparatus for displaying a plurality of topographical maps of brainelectrical activity sensed by a plurality of electrode sensors disposedon a patient's head, wherein said sensors provide an associatedplurality of changeable amplitude sign input activity signals responsiveto said brain electrical activity, said apparatus comprising:processingmeans connected to be responsive to said changeable amplitude sign inputactivity signal for providing an amplified and digitized form of saidinput activity signals; means for providing a video output responsive tosaid amplified and digitized input activity signals, said video outputincluding a set of interpolated input activity signals for positionsbetween the locations of said plurality of sensors with said positionsincluding selected locations along at least two interpolated linesgenerated between adjacent pairs of lines formed by connecting thelocations of said sensors and at least two of said interpolated linesbetween each said adjacent pairs of lines being generated fromdistinguishable appropriate combinations of said input activity signalsand said interpolated input activity signals are generated and displayedline--by--line while a next successive adjacent line for display isbeing generated by said means for providing a video output; and meansfor displaying simultaneously a display of a plurality of saidtopographical maps of said brain electrical activity responsive to saidvideo output.
 17. The apparatus as defined in claim 16 wherein saidplurality of topographical maps comprises a plurality of differentselectable states of said brain electrical activity.
 18. The apparatusas defined in claim 17 wherein said different selectable states comprisean evoked potential response, an integrated time segment of evokedpotential response and a Fourier transform of EEG input activitysignals.
 19. An apparatus for displaying topographical maps of brainelectrical activity of a patient's head comprising:a plurality ofelectrode sensors disposed on said patient's head, said sensorsproviding an associated plurality of changeable amplitude sign inputactivity signals in response to said brain electrical activity;processing means connected to be responsive to said input activitysignals for providing an amplified and digitized form of said changeableamplitude sign input activity signals; means for providing a videooutput responsive to said plurality of amplified and digitized inputactivity signals, said video output including a set of interpolatedinput activity signals for positions between the locations of saidplurality of sensors with said positions including selected locationsalong at least two interpolated lines generated between adjacent pairsof lines formed by connecting the locations of said sensors and at leasttwo of said interpolated lines between each said adjacent pairs of linesbeing generated from distinguishable appropriate combinations of saidinput activity signals; input means for supplying an input signalresponsive to a user input, said input means controlling the informationcharacterized by said video output: and means for displaying saidtopographical maps of said brain electrical activity responsive to saidvideo output, said display means including display processing meanshaving a display memory which can be updated for display of userselected lines of said topographical maps responsive to said inputactivity signal.
 20. The apparatus as defined in claim 19 wherein saidmeans for providing a video output comprises logic means responsive tocomputer software programs for providing said video output responsive tosaid amplified and digitized input activity signals.
 21. The apparatusas defined in claim 19 further including color code means for displayingnear each of said topographical maps at least a portion of apredetermined set of colors, each of said colors appearing on anassociated one of said topographical maps and each of said colors havingan associated fixed relative value within a selected closed data set ofsaid input activity signals.
 22. The apparatus as defined in claim 21wherein said predetermined set of colors is arrangeable for displayalongside a portion of said topographical map.
 23. The apparatus asdefined in claim 21 wherein said predetermined set of colors isarrangeable for display along at least one of a vertical scale and ahorizontal scale.
 24. The apparatus as defined in claim 19 furthercharacterized in that said display includes at least one evokedpotential response waveform plotted near each of said topographicalmaps, each said waveform characteristic of an amplitude and timeresponse for a selected location on said topographical map.
 25. Anapparatus for displaying a topographical map of EEG brain electricalactivity in a plurality of frequency bands of a patient, comprising:aplurality of electrode sensors disposed on a patient's head formeasuring EEG input activity signals at each of said plurality ofelectrode sensors; processing means connected to be responsive to saidinput activity signals for providing an amplified and digitized form ofsaid input activity signals; means for sampling said amplified anddigitized form of said EEG inout activity signals at predeterminedintervals responsive to said amplified and digitized form of said inputactivity signals to provide sampled forms of said EEG input activitysignals; means for performing a Fourier transform of said sampled formsof EEG input activity signals responsive thereto to provide a frequencyband energy output characteristic of the energy in each of saidplurality of frequency bands; computer means responsive to saidfrequency band energy output for generating a set of interpolatedfrequency band energy output signals for positions between the locationsof said plurality of sensors, said output signals generated for saidpositions including selected locations along at least two interpolatedlines generated between adjacent pairs of lines formed by connecting thelocations of said sensors and at least two of said interpolated linesbetween each said adjacent pairs of lines being generated fromdistinguishable appropriate combinations of said input activity signals;and display means for displaying said topographical map responsive tosaid frequency band energy output signals.
 26. The apparatus as definedin claim 25 further including a display of at least one EEG curveplotted near each said topographical map, each said EEG curvecharacteristic of the amplitude within each said frequency band.
 27. Theapparatus as defined in claim 26 wherein said display of EEG curves canbe color coded by positioning selected color coded segments along thefrequency axis of said EEG curve, each of said color coded segmentsassociated with a preselected one of said frequency bands.
 28. Anapparatus for displaying a topographical map of brain electricalactivity sensed by a plurality of electrode sensors disposed on apatient's head, wherein said electrode sensors provide an associatedplurality of input activity signals, said apparatuscomprising:processing means for providing an amplified and digitizedform of said plurality of input activity signals; computer means forproviding a video output responsive to said plurality of amplified anddigitized input activity signals; means for displaying saidtopographical maps of said brain electrical activity responsive to saidvideo output; and input means for supplying an input signal responsiveto a user input and indicator means connected to be responsive to saidinput signal for actuating selected software programs to control saidvideo output on said means for displaying, said indicator means able toselect a line on said topographical map and actuate said computer meansto display amplitudes of said input activity signals along said line.